The present invention relates to a method of manufacturing a magnetic tape cassette, and particularly relates to a method of manufacturing a magnetic tape cassette, the half parts of the body of which are manufactured by plural-color molding.
In a conventional magnetic tape cassette for an audio or video equipment or the like, a pair of hubs on which a magnetic tape is wound are rotatably supported in the cassette body. The body is made of upper and lower half parts, each of which are usually manufactured by the injection molding of a plastic or the like. The body is provided with one or more transparent or semitransparent windows through which the wound state of the magnetic tape or the like can be seen from outside. Even if the whole cassette body is made of an optically transmissive material, the windows are often separately made of another optically-transmissive material. In that case, the windows are set at a higher optical transmissivity than the cassette body itself to more surely perform the proper function of each of the windows. The windows may be shaped in desired forms to produce a design effect.
Each of the windows is manufactured by bonding a separate window member to the cassette body through the use of an adhesive, through a process of ultrasonic welding or the like. However, there is a drawback in that it is necessary to separately manufacture the window member and thereafter to bond it to the cassette body. If the cassette body is made of the same optically transmissive material, there is another drawback in that the bonded portion of the cassette body is so visible as to deteriorate the appearance thereof.
In order to eliminate such drawbacks, a method of manufacturing a magnetic tape cassette through two-color molding has been adopted recently. However, providing the window using the two-color molding method also creates problems. When one or more windows having a relatively complicated form are to be provided, as illustrated by windows 3a and 3b of FIG. 6, cores having the same forms as the windows are moved in the direction of the thickness of the body 2 of the cassette, after the injection molding of the cassette body, so that openings having the same forms as the windows are defined. A plastic for molding the windows is then injected in the direction of the thickness of the cassette body 2 through a direct gate or the like. At that time, slender intermediate portions already molded in the body, such as portion 2a located between the openings 3a and 3b, undergo deformation or color change due to the pressure or heat of the plastic injected into the openings, so that a desired form or appearance cannot be obtained. Countermeasures, such as limiting the movement of the cores so as to hold the slender intermediate portion 2a to prevent it from undergoing the deformation or color change, have been taken in order to solve the problem. However, such countermeasures restrain the form or design of the windows 3a and 3b greatly.